1. Field of the Invention
The invention relates to the field of power steering pumps as used in automotive vehicles and more specifically to the area of improved energy efficiencies in flow control devices that are used to control the delivery of hydraulic fluid to steering assist valves.
2. Description of the Prior Art
In conventional power assist steering systems, many techniques are used to position the location of a spool within a control valve to regulate the delivery of a constant amount of hydraulic fluid from a pump to a steering assist valve. Because the flow from the pump increases or decreases depending on the pump rotary speed, the flow regulation mechanism of the control valve is necessary to maintain a constant flow to the steering assist valve independent of pump rotary speed. In most cases, a by-pass orifice is established in the control valve that allows excess steering fluid to be diverted back to the pump input port or a fluid source. Corresponding control of the position of the spool regulates the flow into the bypass orifice to thereby maintain a constant steering fluid flow delivered to the steering assist valve while the pump is driven at rates that increase or decrease depending only on the speed of the engine or other power source.
In such conventional power assist steering systems the pump provides a relatively high outlet flow at high pressure even when no steering assist is required. One such instance occurs when the vehicle is in a stationary or parked position with the motor running and no steering effort is being applied by the vehicle operator. Similarly, the pump provides a high output flow when the vehicle is moving at a high speed and low power assist is desired to be applied to the actuator. High flow creates higher pressure and increases the torque required to drive the pump. Such drive torque demand on the engine directly affects vehicle horsepower output and fuel efficiency.